1. Field of the Invention
The present invention relates to a fusing apparatus. More particularly, the present invention relates to a fusing apparatus including a fusing roller that fuses an image on a sheet of paper by induced heating.
2. Description of the Related Art
Generally, an image forming apparatus using an electrophotographic method, such as laser printers or digital copying machines, is an apparatus printing a mono-color image or a full-color image by forming an electrostatic latent image by scanning light onto a photosensitive medium charged to a predetermined electric potential. The electrostatic latent image is developed using toner of a predetermined color in a developing unit, and transferring and fusing the developed image onto a sheet of paper. Thus, a mono-color image or a full-color image is printed.
The electrophotographic image forming apparatus can be classified into a wet type image forming apparatus and a dry type image forming apparatus.
The wet type electrophotographic image forming apparatus uses a developer that is made by distributing powder toner in a liquid carrier. The dry type electrophotographic image forming apparatus uses a binary developer in which powder carrier and toner are mixed, or a single developer without the carrier. Hereinafter, the dry type electrophotographic image forming apparatus will be described, and the developer will be referred to as a toner.
FIG. 1 is a transverse cross-sectional view of a fusing apparatus using a halogen lamp as a heat source, according to the conventional art. FIG. 2 is a longitudinal cross-sectional view of the apparatus along line I-I″ of FIG. 1.
The fusing apparatus 10 includes two cylindrical fusing rollers 11 and 12 formed of aluminum. Both ends of the fusing rollers 11 and 12 are supported by bearings 14 that contact each other in a lengthwise direction. Coating layers 13 are formed on surfaces of the fusing rollers 11 and 12 for forming a nip where heat transmission to the images is performed, and improving releasing of the images.
A heating unit 15 uses a halogen lamp as a heat source and is connected to an external power source (not shown) to generate heat. The heating unit is installed in each fusing roller 11 or 12. The heating unit 15 is separated from the fusing roller 11 or 12, and air is filled therebetween.
When electric current provided from the external power source (not shown) is applied to both ends of the heating unit 15, the heating unit 15 generates radiation energy. The generated radiation energy is transmitted to inner walls of the fusing rollers 11 and 12 through the air, and a light/heat conversion layer formed as a black body converts the radiation energy into heat energy. The converted heat energy is transmitted to the image 21 on a recording medium 20 that passes through the nip, where the fusing rollers 11 and 12 contact each other, and through the fusing rollers 11 and 12 and the coating layer 13. Therefore, the image 21 is melted by the heat energy, and fused on the recording medium 20.
However, the fusing apparatus using the halogen lamp as the heat source has the following problems.
When the power source is supplied to perform the printing operation, a long warm-up time is required until the temperature reaches the fusing temperature from the normal temperature. A user should wait until the fusing roller reaches the fusing temperature before the printing operation can be performed.
Additionally, since the halogen lamp and the fusing roller are separated from each other and air is filled therebetween, the heat generated by the halogen lamp heats the fusing roller by radiation, and passes through the fusing roller by conduction. Therefore, the heat transmission speed is low, and heat efficiency is lowered.
The halogen lamp is connected to an external power source to receive power from the external power source. Contact resistance may be generated at a contact portion where the halogen lamp is connected to the external power source. The contact resistance may oxidize the contact portion or make the contact portion corroded, thus power may not be supplied from the power source efficiently.
Accordingly, a need exists for an improved fusing roller that reduces contact resistance and increases the efficiency of induced heating.